8474b70c3a
We were inconsistent, but marking them up as constants makes more sense then as variables.
191 lines
9 KiB
XML
191 lines
9 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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This file is part of systemd.
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Copyright 2013 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="sd_bus_message_get_monotonic_usec" conditional="ENABLE_KDBUS">
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<refentryinfo>
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<title>sd_bus_message_get_monotonic_usec</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_bus_message_get_monotonic_usec</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_bus_message_get_monotonic_usec</refname>
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<refname>sd_bus_message_get_realtime_usec</refname>
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<refname>sd_bus_message_get_seqnum</refname>
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<refpurpose>Retrieve the sender timestamps and sequence number of a message</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_bus_message_get_monotonic_usec</function></funcdef>
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<paramdef>sd_bus_message *<parameter>message</parameter></paramdef>
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<paramdef>uint64_t *<parameter>usec</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_message_get_realtime_usec</function></funcdef>
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<paramdef>sd_bus_message *<parameter>message</parameter></paramdef>
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<paramdef>uint64_t *<parameter>usec</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_message_get_seqnum</function></funcdef>
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<paramdef>sd_bus_message *<parameter>message</parameter></paramdef>
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<paramdef>uint64_t *<parameter>seqnum</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_bus_message_get_monotonic_usec()</function>
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returns the monotonic timestamp of the time the
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message was sent. This value is in microseconds since
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the <literal>CLOCK_MONOTONIC</literal> epoch, see
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<citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
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for details.</para>
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<para>Similar,
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<function>sd_bus_message_get_realtime_usec()</function>
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returns the realtime (wallclock) timestamp of the time
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the message was sent. This value is in microseconds
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since Jan 1st, 1970, i.e. in the
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<literal>CLOCK_REALTIME</literal> clock.</para>
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<para><function>sd_bus_message_get_seqnum()</function>
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returns the kernel-assigned sequence number of the
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message. The kernel assigns a global, monotonically
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increasing sequence number to all messages transmitted
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on the local system, at the time the message was
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sent. This sequence number is useful for determining
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message send order, even across different busses of
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the local system. The sequence number combined with
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the boot ID of the system (as returned by
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<citerefentry><refentrytitle>sd_id128_get_boot</refentrytitle><manvolnum>3</manvolnum></citerefentry>)
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is a suitable globally unique identifier for bus
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messages.</para>
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<para>Note that the sending order and receiving order
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of messages might differ, in particular for broadcast
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messages. This means that the sequence number and the
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timestamps of messages a client reads are not
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necessarily monotonically increasing.</para>
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<para>These timestamps and the sequence number are
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attached to each message by the kernel and cannot be
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manipulated by the sender.</para>
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<para>Note that these timestamps are only available on
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some bus transports, and only after support for them
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has been negotiated with the
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<citerefentry><refentrytitle>sd_bus_negotiate_timestamp</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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call.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On success, these calls return 0 or a positive
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integer. On failure, these calls return a negative
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errno-style error code.</para>
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<para>On success, the timestamp or sequence number is
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returned in the specified 64-bit unsigned integer
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variable.</para>
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</refsect1>
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<refsect1>
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<title>Errors</title>
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<para>Returned errors may indicate the following problems:</para>
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<variablelist>
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<varlistentry>
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<term><constant>-EINVAL</constant></term>
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<listitem><para>A specified parameter
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is invalid.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENODATA</constant></term>
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<listitem><para>No timestamp or
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sequence number information is
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attached to the passed message. This
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error is returned if the underlying
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transport does not support
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timestamping or assigning of sequence
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numbers, or if this feature has not
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been negotiated with
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<citerefentry><refentrytitle>sd_bus_negotiate_timestamp</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>The
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<function>sd_bus_message_get_monotonic_usec()</function>,
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<function>sd_bus_message_get_realtime_usec()</function>,
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and <function>sd_bus_message_get_seqnum()</function>
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interfaces are available as a shared library, which
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can be compiled and linked to with the
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<constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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file.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_negotiate_timestamp</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_id128_get_boot</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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